Do impact windows qualify for the home energy credit?

They can, but not all will qualify.  Exterior residential windows or skylights must meet the ENERGY STAR Most Efficient criteria to be eligible for the 25C Federal Tax Credit.  

The credit can cover both the purchase and installation costs for heat pumps, energy efficient AC units, furnaces/ boilers, water heaters, biomass stoves/ boilers, and electric panel/circuit board upgrades.   For building envelope components (insulation, doors, windows, skylights), only the purchase can be covered. Requesting an itemized invoice or receipt from your contractor/installer can be helpful. 

For more information, see IRS Pub 5967

And Energy.gov